0380-insert-delete-getrandom-o1.rs

use rand::seq::SliceRandom;
use std::collections::HashMap;

pub struct RandomizedSet {
    mp: HashMap<i32, i32>,
    arr: Vec<i32>,
}

impl RandomizedSet {
    fn new() -> Self {
        RandomizedSet {
            mp: HashMap::new(),
            arr: Vec::new(),
        }
    }

    fn insert(&mut self, val: i32) -> bool {
        let res = !self.mp.contains_key(&val);
        if res {
            self.mp.insert(val, self.arr.len() as i32);
            self.arr.push(val);
        }
        res
    }
    fn remove(&mut self, val: i32) -> bool {
        let res = self.mp.contains_key(&val);
        if res {
            let idx = *self.mp.get(&val).unwrap();
            self.mp
                .entry(*self.arr.last().unwrap())
                .and_modify(|v| *v = idx);
            self.arr.swap_remove(idx as usize);
            self.mp.remove(&val);
        }
        res
    }
    fn get_random(&self) -> i32 {
        *self.arr.choose(&mut rand::thread_rng()).unwrap()
    }
}